This invention relates to a process for the wet-surface treatment of semiconductor wafers, in which aqueous phases containing one or more chemically active substances in solution are caused to act on the surfaces.
The constantly increasing miniaturization in the production of electronic components has resulted in increased requirements imposed on the surface quality of semiconductor wafers made from materials such as silicon, gallium arsenide and indium phosphide. These requirements apply not only to the geometrical quality of the wafer surfaces, but also to their cleanliness, chemical finish and freedom from particle contamination.
In order to control these parameters cleaning processes were developed wherein, after a polishing operation which guarantees the geometrical perfection of the semiconductor surfaces, a sequence of treatment steps is carried out in which various aqueous agents act on the wafer surfaces. Most of these processes originate essentially from a cleaning process which was specified by W. Kern and D. A. Puotinen in RCA Reviews 31, 187 (1970) and which comprises a sequence of rinsing, hydrophilizing and hydrophobizing steps. Generally, aqueous solutions of ammonia, hydrogen chloride, and hydrogen fluoride are used as agents, and hydrogen peroxide is used as an oxidizing component.
It is also essential that the solutions used fulfil the strictest purity requirements, with regard to the proportion of foreign ions or the freedom from particles contamination. Thus, at great expense, the solutions are free, as much as possible, from particle contamination even during their production by filtration operations. They are then transported in special containers and then poured into cleaning baths or spraying systems, or into upstream reservoirs, with special precautions being taken. Additional filtration devices may be provided in the existing inlet or outlet pipes.
However, these steps have the disadvantage in that, on the one hand, the finished solutions may have to be transported in large quantities over long distances, adding to the expense and the risk of contamination. Moreover, where a multiplicity of consecutive treatment steps involves various solutions, a correspondingly large number of immersion baths has to be provided. The composition of these baths is subject to variations due to their chemical reaction with the substrates and/or the volatility of chemically active substances. In conventional spray cleaning processes, it is necessary to keep extensive stocks of chemicals for the various solutions. In addition, the residues of the preceding treatment step, in particular in the inlet pipes, have to be removed using elaborate intermediate washing steps before the subsequent step can be initiated.